In recent years, with continuous increasing of demand for network applications, especially rapid development of high definition video services and high speed data services, requirement on network bandwidth becomes much higher. The conventional communication system is being developed towards 100 G bit/s or even 400 G bit/s. In a high speed DWDM communication system, a tunable laser of high performance plays an important role, and a high speed coherent communication system needs tunable lasers that meet characteristic requirements such as broad tuning range, stability in high frequency, narrow line width, high power, low power consumption, small volume and the like.
At present, the tunable lasers that meet the above characteristic requirements mainly include a monolithic integrated semiconductor tunable laser, an external cavity adjustable laser and a silicon based laser or the like. The monolithic integrated semiconductor tunable laser implements tuning of wavelength by changing refractive index of grating area or changing temperature of die. It has advantages of small volume, good stability and the like, and has been applied in commercial products used in a high speed multi-channel coherent communication system. However, technique for a monolithic integrated multi-section waveguide is very complicated, and fabrication of a grating with complex structure is even more difficult, so that the monolithic integrated semiconductor tunable laser cannot be mass produced with a low cost. A conventional external cavity adjustable laser may select different oscillating wavelengths by changing position of a diffraction grating for the external cavity in a mechanical way. It has advantages such as large tuning range, narrow line width and the like, and is also applied in commercial products used in the high speed multi-channel coherent communication system. However, the conventional external cavity adjustable laser has a relatively large volume and miniaturization thereof is difficult. In order to satisfy requirements of practical application, a micro-mechanical tuning device has been proposed in recent years, which has a greatly reduced volume and a high tuning speed, but a poor stability. The silicon based photoelectric integration device has a very attractive future. However, as silicon is an indirect band gap material which has very low luminous efficiency, research of the silicon based light emitting device has encountered difficulties that are almost impossible to overcome. Emergence of silicon based hybrid laser brings great inspiration to research of silicon based photonics, and with in-depth study on the silicon based photon device, break-though progresses have been made on researches of silicon based long wavelength detector, silicon based optical modulator, and optical switch. However, as compared with other silicon based photon device, silicon based luminescence device and laser still need further development. Nowadays, a popular concept is to integrate a III-V laser gain die and a silicon based optical waveguide chip to construct a hybrid external cavity laser. The present application proposes a technical solution of an arrayed waveguide grating based hybrid integrated laser having adjustable external cavity, which produces a tunable laser by coupling of end surfaces of the optical waveguide chip and the semiconductor gain die. The technical solution can overcome limitations of complex process for the monolithic integrated semiconductor laser. Meanwhile, since the external cavity uses an integrated chip, the technical solution can solve the problem of poor stability with the conventional external cavity adjustable laser caused by the external cavity including a number of components. In addition, the laser of the proposed structure has a higher integration level, which improves efficiency of coupling package and benefits the subsequent mass manufacture.